1. Field of the Invention
The present invention relates to a vehicle and a method for controlling engine start in a vehicle.
2. Background Art
Hybrid electric vehicles (HEV's) utilize a combination of an internal combustion engine with an electric motor to provide the power needed to propel a vehicle. This arrangement provides improved fuel economy over a vehicle that has only an internal combustion engine. One method of improving the fuel economy in an HEV is to shutdown the engine during times that the engine operates inefficiently, and is not otherwise needed to propel the vehicle. In these situations, the electric motor is used to provide all of the power needed to propel the vehicle. When the driver power demand increases such that the electric motor can no longer provide enough power to meet the demand, or if the battery state of charge (SOC) drops below a certain level, the engine must start quickly and smoothly in a manner that is nearly transparent to the driver.
One method of controlling engine start in an HEV is described in U.S. Pat. No. 7,370,715 issued to Colvin et al. on 13 May 2008, which is hereby incorporated herein by reference. In an HEV, the engine may be initially cranked by an electric motor that may also output torque to propel the vehicle. When the vehicle is being propelled by the motor, and an engine start is requested, it is desirable to control the powertrain—i.e., the engine, motor, transmission, etc.—such that torque is transferred from the motor to the engine without substantially disrupting the flow of torque from the motor to the vehicle wheels. This can be particularly problematic when the engine is first being cranked because this is when the engine torque requirements are highest and torque disturbances can occur. Therefore, a need exists for a vehicle, and a method for controlling engine start in a vehicle, that reduces or eliminates driveline torque disturbances when the engine is started.